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To find how the resistance of a wire changes as we change the length.

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Aim: To find how the resistance of a wire changes as we change the length.

Hypotheses: Resistance is measured in ohms and found from this formula:

R= V


V= Potential difference measured in volts.

R= Resistance measured in ohms.

I= Current measured in amps.

Resistance measure the difficulty for current to pass though a component. In a metal the atoms are packed closely together and can only vibrate.


Every atom has one free electron not used for bonding. This free electron is able to move past the other atoms of metal. It does not move through freely as it ‘knocks’ into their atom’s electron clouds. This creates a ‘drunken’ path.

        When a voltage is put across the metal the free electrons will try to move to the positive end. The more electron clouds there are, the harder it will be for the free electron to move to the positive end. This is resistance. The more electrons an atom has, the further away its electron cloud stretches. The more electron clouds there are, the higher the resistance.  

I think that if we increase the length of the wire, the amount of resistance will also increase. I also think that if the length is shortened so the resistance will fall. This is because; in the first instance the amount of atoms increases. This means that there are more electrons, meaning the free electrons have more chance of bumping into the electron clouds.

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The difference between 50cm and 51cm is too small. Doing the experiment with 1cm intervals of constantan would not be beneficial. At a 5cm gap there is still a small difference in the resistance. Only when there is a 10cm interval does it become beneficial to do the experiment. We shall, therefore, do the experiment with 10cm intervals from 20cm to 70cm. (20cm-30cm-40cm-50cm-60cm-70cm).


        In our experiment we shall use the following apparatus:

1 power pack.

1 ammeter.

1 voltmeter.

A 100cm ruler.

2 crocodile clips.

5 wire leads.

A 1m length of constantan wire.

        We shall set up the above apparatus as shown in the diagram below.


We shall conduct the experiment as follows.

  1. Set up the apparatus as above.
  1. Use the ruler to measure out a set amount of constantan wire. Attach to croc clips (20cm to start with, and then as instructed in the pilot).
  1. Switch the power pack on to 1 volt. Read off at the ammeter and the voltmeter. Divide the reading from the voltmeter by the reading on the ammeter to find the resistance (as suggested by the equation in the hypothesis).
  1. Repeat for the different lengths of wire as explained in the results for the pilot section above.
  1. Be sensible with equipment at all times!
  1. Repeat. The end of the experiment is nigh.

In the experiment there are four variables we can control whilst conducting the experiment.

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        If the wire had been heated up then there would have been a curving graph. This means that there would not have been direct proportionality. Indeed if any of the other variables namely length, width, or material had been changed then the results would be different to the ones that I collected. I could have investigated with each one of these variables in order to find different sets of results.

        In order to further investigate there are two things that we could have done. First we could investigate with more lengths of constantan wire. Ideally we would use lengths of 1cm intervals between 1cm and 100cm. We could, as a further task, investigate whether all materials are directly proportional to their resistance.  

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